In the field of rolling flat products there is an increasingly marked tendency on the part of constructors to seek solutions for the high efficiency production of thin and ultra-thin rolled stock leaving the finishing train at ever greater speeds.
The thinner the strip is, the greater must be the speed at which it leaves the finishing train; this is because it is necessary to maintain the rolling temperature and the winding temperature within well-defined fields, for both technological and metallurgical reasons.
It is well-known that there is an increasing demand on the part of users for finished strip and sheet with a thickness of less than 1 mm, to as little as 0.5.div.0.6 mm, since these values offer two possibilities:
cold rolling can be eliminated and the hot rolled product may be used directly, or after pickling. This solution uses thicknesses of more than 0.6 mm. PA1 the rolling passes in cold rolling mills and also any intermediate heat treatments may be reduced. In this case thicknesses of less than 0.6 and as little as 0.1 mm are used.
Competition between the producing companies is linked, not only to the quality of the final product, but also to the speed with which the strip/sheet can be extracted from the finishing train and wound onto the respective collection means. The greater the speed, the higher the production.
In the light of the fact that there are more and more endless rolling systems, even in hot rolling mills, it has become evident that one of the main obstacles against obtaining, in a highly efficient and continuous manner, speeds of above 10 metres per second to as much as 20 metres per second and more, is that of coiling the strip/sheet as it leaves the finishing train.
For this purpose, the state of the art has developed a winding reel of the rotary type, which is placed at the outlet of the finishing train, and is called a carousel reel.
The winding reel includes at least two mandrels which exchange their working position alternately and continuously, that is to say the position in which they wind the strip as it leaves the finishing train and the position in which they wait for the subsequent strip.
With this solution the winding conditions are always the same, regardless of which mandrel the strip is wound onto.
This does not happen in conventional downcoilers where slight differences in functioning (which are difficult to compensate, because they have origins which cannot be controlled), as well as differences in the path followed by the strip, can cause different winding conditions which have an effect on the geometric quality of the coil and on the metallurgical quality of the strip.
In the winding cycle of the carousel winding reel, after the strip has started winding onto the first mandrel in the working position and a desired number of spirals have been wound, the reel rotates and, while the first mandrel continues and concludes the winding, the second mandrel places itself in the working position while it waits for the next strip.
At this point a shears element intervenes; it is placed between the finishing train and the entrance to the winding reel, and shears to size the strip with respect to the continuous rolled stock and thus obtains coils of finished weight.
Carousel winding reel such as are known to the state of the art therefore include at least a pair of winding mandrels associated with a supporting structure which is governed by a drive mechanism suitable to make it rotate through an arc of at least 180.degree., in order to perform the variations in the position of the said mandrels according to the step of the winding cycle.
In the state of the art the drive mechanisms for the mandrels include complex kinematisms with off-axis motors fixed to the floor which supply motion by means of kinematic chains including respective transmission gears, or which use transmission systems with a universal joint or similar.
Although these proposals of the state of the art are satisfactory for particular and limited applications, they have not shown themselves to be efficient enough in hot rolling mills where the radiance of the strip can cause thermal deformations of the structure and where it is necessary to begin winding at the same operating speed, something which never happens in cold rolling mills.
Moreover, these solutions do not obtain high productivity winding cycles with the extremely high outlet speeds of the strip/sheet from the finishing train, speeds of up to 20 metres per second and more, which present-day technology can achieve and with the ever more reduced thickness of the strip, as required by the market.
The limitations of the proposals known to the state of the art concern the resistance to stresses of a mechanical, heat and electric nature, given the violent slopes of acceleration/deceleration to which the mandrels are subjected during the steps preparatory to winding and at the end of winding.
To be more exact, the mandrel is subject to high torsional stress because of the axial distance with respect to the motor.
Other disadvantages concern the complexity of assemblydisassembly, the difficulty of maintenance operations, premature wear of the more delicate components of the kinematic chain and other problems.
JP-A-61.124478 teaches that every shaft of each mandrel is associated with an electric motor, the stator being made solid with the rotatable structure.
By extracting the mandrel shaft, which operates on bearings on the rotatable structure, it is possible to remove the electric motor once the stator has been disconnected from the rotatable structure.
This teaching is interesting, but there are considerable problems connected with the day-to-day maintenance of the mandrel, which is the object of frequent maintenance work, and with the non-routine maintenance of the motor.
Moreover, there are problems to arrange the rotor and the stator coaxial, and to arrange the mandrel shaft and the rotor coaxial.
EP-A-0.812.634, precisely to reduce the problems typical of JP-A-61.124478, teaches that the rotatable structure should have seatings onto which electric motors complete with casings are applied.
The casing bears the main bearings of the rotor and the assembly structure allows to extract the mandrel, extract the rotor alone and also with the mandrel and to disassemble the casing to remove the stator too.
This solution is also interesting, but has disadvantages such as the increased weight caused by the casings of the motor, the alignment of the main bearings of the rotor, the reduced rigidity of the structure, since the drawing force of the sheet or strip is supported by the individual casing, the connection between the casing and the rotatable structure when there are continuous vibrations and stresses, the centrifugal force which is discharged on the casing and on the clamping means.
The present applicants have designed, tested and embodied this invention to overcome the shortcomings of the state of the art and to achieve other advantages as will be shown hereinafter.